Drill grinding machine



March 25, 1958 E. w. HILLIER 2,827,741

DRILL GRINDING MACHINE Filed Sept. 29. 1955 2 Sheets-Sheet 1 INVENTOR. 10152 W. HILL/E12 March 25, 1958 E. w. HILLIER 2,827,741

DRILL GRINDING MACHINE Filed. Sept. 29, 1953 2 Sheets-Sheet 2 JNVENTOR. 152mm MA az/ae United States Patent DRILL GRINDING MACHINE Elmer W. Hillier, Culver City, Calif., assignor of one-bait to Robert K. Thomas, Venice, Calif.

Application September 29, 1953, Serial No. 332,999

Claims. (Cl. 51-96) My invention relates generally to drill grinding machines and more particularly to a universally adjustable grinding machine which is especially adapted to perform split center grinding.

Conventional twist drills are usually ground with a generally conical point, the solid body portions between the flutes forming cutting lips and heel surfaces which intersect at the central portion of the drill designated as the web, to form a sharp chisel edge known as the dead center of the drill. in a properly ground drill, the heel portions are sloped back from the cutting lips at a slight angle from the normal to the drill axis, known as the lip clearance angle. It is very important that the drill have the proper lip clearance angle for good cutting action.

in addition to the usual grinding of the drill point, it is often desirable to grind the point with a split center grind wherein the width of the dead center edge of the drill is reduced to a point by grinding away the back portion of the heel surface of the drill at a steeply tapered angle. Drills ground with such a split center point have a finer cutting action for certain types of metals, and are widely used in the aircraft industry among others.

An embodiment of this invention provides a single grinding machine which is capable of performing all of the operations for grinding a conventional drill point and a split center point. Furthermore, the machine is designed for very simple and rapid manual operation whereby a large number of drills can be reground in a short time.

With the foregoing in mind, it is a major object of my invention to provide an improved drill grinding machine which is adapted for grinding both conventional and split center points.

Another object of the invention is to provide a drill grinding machine adapted for simple and rapid manual operation and which is easily adjustable for grinding any type of twist drill.

it is also an object of the invention to provide a drill grinding machine having a drill holder pivotally mounted in such a manner as to grind the heel surfaces of the point with the desired lip clearance angle.

A further object of the invention is to provide an adjustable drill stop finger having a stepped seat for limiting rotation and forward movement by the drill point.

Still another object of the invention is to provide adjustable stop means for limiting the pivotal movement of the drill holder in grinding to form a split center point.

These and other objects and advantages of my invention will become apparent from the following detailed description of a preferred form thereof, and from an inspection of the accompanying drawings in which:

Figure l is a perspective view of a preferred embodiment of the grinding machine;

Figure 2 is an enlarged detail of the drill holder and stop finger;

Figure 3 is a partial section taken in the direction of the arrow 3 of Figure 2;

Figure 4 is a partial side elevation taken in the .direction of arrow 4 of Figure 2;

Figure 5 is a view similar to Figure 4 showing the drill holder pivoted through a grinding swing;

Figures 6 and 7 are enlarged details showing the pivoted relationship of the drill point to the grinding Wheel;

Figure 8 is a view similar to Figure 2 showing the drill holder in position for split center grinding;

Figure 9 is a partial side elevation showing the initial pivotal position of the drill holder for split center grinds;

Figure 10 is a view similar to Figure 9 showing the drill holder pivoted against the stop;

Figures 11 and 12 are enlarged details showing the pivotal relationship of the drill point to the grinding wheel;

Figure 13 is a detail showing the angular relationship of the stop finger and drill point; and

Figure 14 is a view of the completed split center point taken in the direction of the arrow 14 in Figure 13.

Referring now to the drawings, it is advantageous to consider the view of a twist drill 20 ground with an ordinary conical point as is best seen in Figures 2 and 3, and with a split center point as is best seen in Figures 13 and 14. Drill 20 is formed with opposed flutes 21 which separate body portions 22 extending with a conventional twist or rake angle along the length of the drill. To provide clearance for the body portion 22, slightly raised margins 23 extend along the leading edge of the body portions. At the point of the drill, cutting lips 24 are formed on each of body portions 22, and behind the cutting lips are heel surfaces 25 which slope away from the normal to the drill axis at a slight angle to provide lip clearance.

Thus the drill point has a generally conical point, the cutting lips 24 being at an angle with the drill axis, this cutting angle of the drill being usually about 59 for general purpose work, and the heel surface 25 sloping away from the cutting lips 24 at a lesser lip clearance angle .of approximately 12 to 15. The intersection of the heel surfaces 25 results in the formation of a central chisel point or dead center 26 which extends across between the cutting lips 24.

The drill point thus far described has the conventional grind as illustrated in Figures 2 through 7. However, as an additional refinement for certain kinds of work it is desirable to provide a split center grind to reduce the width of the dead center 26 to substantially a'point. This is done by grinding a sharply tapered surface 27 on the back of each of the heel surfaces 25. These surfaces 27 are cut so as to intersect on the axis of the point as seen in Figures 13 and 14, so that the dead center 26 has a triangular side profile. The drill grinding machine herein described is adapted to perform both conventional and split center grinding and is thus particularly advantageous.

As is best seen in Figure l, the grinding machine has a solidly mounted base 39 which supports on one end an electric motor 31. The shaft of motor 31 extends transversely and carries rotatably therewith inner and outer grinding wheels 32 and 33, respectively. Mounted beneath grinding wheels 32 and 33 is a carriage or table 34 which is adapted for horizontal movement relative to base 30. A screw feed for movement of carriage 34 along the length of base 30 is controlled by a handle 36, and a similar cross screw feed is controlled by a handle 37. By the use of handles 36 and 37, the position of carriage 34 relative vto grinding wheels 32 and 33 may be accurately adjusted.

Secured to the top of carriage 34 and extending upwardly'alongside the outer grinding wheel 33'is a bracket 39 which is of generally rectangular shape and has a front wall .whichis approximately in line with the front edges 'ofgrindingwheels 32 and 33.; Bracket 39 has rigidly secured to the front thereof a journal bearing 49 through which is extended a" shaft 41 having a' forwardly extending lever arm 42. Shaft 41 extends substantially parallel to the shaft of motor 31.

In order'to position a, drill 29 in proper relationship to grinding wheels 32 and 33, a drill holder 44 is mounted upon shaft 41-. Holder 44is of elongatedcylindrical shape and has a transverse bore 45 .in which is fitted a remoyable sleeve or bushing 46. Bushing 46 is bored to slidably receiv a drill 20 therethrough and different bushings maybe inserted in holder 44 for use with different size drills. As is best seen in Figure 2, drill lies substantially parallel to the plane of grinding wheels 32 and 33 when extended through bushing 46.

g Holder 44 does not extend coaxial with shaft 41 but ismounted eccentrically thereon by means of a hub 47 which is Welded or otherwise afiixed to the side of the innerfend portion of the shaft. Manual swinging mo tion of lever 42 causes pivotal movement of shaft 41, and accordingly swingingor pivotal'move'ment of holder 44. However, the motion of holder 44 is eccentric to the axis of shaft 41 for the purpose of providing the proper lip clearance angle as will later'be described.

The point of drill 20 extends forwardly through holder 44, and in order to accurately position the point both rotationally and longitudinally, a stop finger 50 is mounted ahead of the holder. Finger 50 is formed as an elongated rectangular bar having a lengthened channel or slot 51 which faces rearwardly towards the point of drill 20'and is adapted to form a seat for engagement with one of the cutting lips 24 and the adjacent heel surface 25. Finger 50 is supported for transverse sliding'movement in ahead 52 and is adjustably locked in position by a set screw 53. 7

Head 52 is rigidly secured at right angles to an elongated rod or arm 54 which extends rearwardly through thebottom of channel 51 to limit rotation of the drill, while the adjacent heel surface 25 abuts the back wall of the channel, as seen in Figure 2, to limit the forward or longitudinal movement of the drill. The opposed cutting lip 24 and heel surface 25 are then positioned to engage against the surface of wheel 33 upon pivotal movement of holder 44. 7

Movement of holder 44 is illustrated in Figures. 4 to 7, the shaft 41 initially being in the position shown in Figure 4, with the point of drill 20 spaced from the surface of wheel 33. Drill 20 is held manually against stop finger 50 by one hand of the operator, leaving the other hand free to move lever 42. As lever 42 is pulled upwardly, drill 20 swings downwardly through an are such as to engage against the surface of wheel 33. The resulting grinding action puts a sharp edge on cutting lip 24 and also cuts the adjacent heel surface 25. Figure 5 shows the position of holder 44 and drill 29 when the latter is in contact with the surface of wheel 33.

The relationship between holder 44 and pivot shaft 41 is such that drill 20 lies below the axis of the pivot shaft.

Accordingly, as is seen in Figures 6 and 7, the heel surface 25 is ground on an are about the pivot axis rather than the drill holder axis and is tapered back away from the cutting lip 24. The displacement of the pivot axis a from the axis of drill 2% is such that heel surface 25 is at I desired lip clearance angle.

holder .44 andis both longitudinally and rotatably adjustable thereinlI A set screw 55 is adapted to lock arm 54 relative to holder, 44. By adjustment of finger relative to head 52, .and arm 54 relative to holder. 44, theposition of stop seat channel. 51 may be accurately adjusted. in proper relationship to the point of drill 20.

As will be remembered, themaehine is capable of grinding both a conventional point and the split center refinement thereof. In'any event, the drill 20 is ground with a 'conventionalpoint first, and. thesteps in performing this operation are illustrated infFigures 2- through 7. Grinding wheel 33 asillustrated has a beveled peripheral edge which is used asthe grinding surface. In order to make use of the proper surface of wheel 33, carriage 34 is first shifted horizontally by the f eed screw handles 36 and 37 so as to bring holder. 44 into the relationship with wheel 33 shown in Figure 2 It should be noted I that when drill 2.0a extended through holder 44 it lies substantially parallel to the plane of wheel 33 so that the cutting lips 24 and heel surfaces 25 are adapted to be ground 05 at an angle with the axis of the drill as determined by the bevel angle of theedge of wheel 33. l The finger 50 is then positioned by adjustment of the finger relative to head 52, and arm 54 relative to holder 44L 4 Forward. movement of'drill 20 is-limited so that the drill point just slightly intersects with the peripheral surface of wheel 33 when the holder '44- is swung through a pivotal are by lever. 42. The depth of cut to be taken upon the point of drillZd varies in accordance with conventional grinding practice.

As. is best seen in Figure 3, finger 5G is positioned substantially horizontally and is adjusted transversely. so that the axis ofdrill 2t) overhangs the end thereof. In this position, one of the drill lips 24 is adapted to engage an angle with the normal to the drill axis equal to the It might also be noted that the grinding streaks or ridges formed onthe heel surface 25 extend back away from cutting lip 24 rather than transversely thereacross. Thus, heel surface 25 has the minimum binding friction with a work piece and the drill operates more smoothly.

As can be appreciated, both of the cutting lips 24 and heel surfaces 25 must be ground, and this is done by reversibly rotating the position ofthe drill point relative to stop finger 50. The operator merely releases his hand pressure on drill 20, pulling it back sli htly. and then rotating it to engage the diametrically opposed cutting lip 24 and heel surface 25 against thestop channel 51. A generally similar procedure can be followed for grinding a drill with any number of cutting lips. One important advantage of the machine which can now be understood, is the simplicity and rapidity with which the rinding operation may becarried out. The drill 2% is eiy held in place by hand while being positioned by the holder 44 and finger 59. This is in direct contrast with most prior grinding machines wherein the drill is locked in place by mechanical means which must be released after each grinding step.

In Figures S'through 14, the additional steps for grinding a split center drill are illustrated. For this operation the position of carriage 34 is shifted so as to bring holder 44 in front of the other grinding wheel 32 which is formed with a straight peripheral surface lying parallel. to the axis of the wheel. As is best seen in Figure 8, drill 20 is extended so that the center of the drill is approxi mately aligned with one side of wheel 32. The purpose of these grinding steps is to cut the tapered surfaces 27 away from the heel surfaces 25 so as to reduce the width of the dead center 26. This necessitates-shifting the position of stop finger 50 and limiting the depth of cut on surfaces 27 as will now be described.

As is best seenin FigureflS, the stop finger 55 is tilted downwardly an amount which is indicated by the arrow in Figure 13 by rotation of arm 54 relative to holder 44, so that a cutting lip 24 contacts the stop seat 53 at a substantial angle with the horizontal. The rotational position of drill 20. is thus adjusted was to bring the dead center 26 into substantial alignment with the plane of the side of grinding wheel 32. Preferably, the dead center 26 lies at a slight angle with the plane of Wheel 32 as shown, so as to undercut-the surfaces 27 beneath the deadcenter.

With drill 20 in the angular position just described,

the holder 44 is pivoted downwardly as seen in Figures 1 1 and 12 to grind the surfaces 27. The grinding of one of the surfaces 27 cuts away half of the dead center 26 as shown in Figure 12. Drill 20 is then rotated through 180 to bring the opposite cutting lip 24 into contact with stop finger 50 and the other surface 27 is ground. This completes the cutting away of dead center 26 so as to result in the split center point as illustrated in Figures 13 and 14.

As can be understood, the surfaces 27 should be ground accurately to a depth so that they just intersect with the central point of dead center 26. In order to accomplish this result, the holder 44 is provided with adjustable stop means which limit the pivotal movement of the holder relative to carriage 34. As seen in Figures 9 and 10, the pivot shaft 41 is provided with an upstanding bracket 57 which is fixed for pivotal movement therewith. Threadedly engaged through bracket 57 is a stop screw 58 which extends inwardly and is adapted to contact the bearing member 49. Screw 58 is adjusted so as to just engage hearing it! when surface 27 is cut to the proper depth as seen in Figure 10. During the previous grinding operation which was first described, screw 58 is backed off as shown in Figures 4 and 5, so that it does not interfere with the pivotal movement of holder 44.

From the foregoing it can be understood that I have provided a grinding machine which is capable of grinding both a conventional and split center drill point. While I have described a preferred embodiment of the machine in some detail, it will be understood that changes and modifications of design may be made without departing from the scope of the invention. Therefore, I do not wish to be restricted except as defined in the appended claims.

I claim:

1. A drill grinding machine which includes: rotatable abrasive means having -a first contoured grinding surface and a second contoured grinding surface, said second grinding surface being differently contoured from said first grinding surface and being cooperatively related thereto; a support carriage adjustably mounted for movement between said grinding surfaces; a drill holder adapted to slidably receive the shank of a drill to position the drill point against either of said grinding surfaces; a stop finger mounted on said holder to engage with a cutting lip of said drill for limiting forward movement and rotation of said drill; and feeding means pivotally mounting said holder on said carriage, said feeding means having its pivotal axis perpendicular to and eccentrically displaced from the axis of said drill such that pivoting of said means to swing said drill from a position with a heel surface trailing portion engaging said abrasive means to a position with the leading portion of said heel surface engaging said abrasive means causes said drill to be slightly withdrawn with respect to said abrasive means, and said drill holder and feeding means cooperating with said first contoured grinding surface to grind the drill lips and the heel surfaces with the desired lip clearance angles, and cooperating with said second contoured grinding surface to remove a particular portion of said heel surfaces for splitting the center of said drill.

2. A drill grinding machine which includes: rotatable abrasive means having a first contoured grinding surface and a second contoured grinding surface, said second grinding surface being differently contoured from said first grinding surface and being cooperatively related thereto; a support carriage adjustably mounted for movement with respect to said abrasive means; a drill holder having a bore adapted to slidably receive the shank of the drill therethrough to position the drill point against said grinding surfaces; at stop finger mounted on said holder projecting forwardly and turning transversely on said drill and having a stepped surface adapted to engage with a cutting lip of the drill for limiting forward movement and rotation of said drill; feeding means pivotally mounting said holder on-said carriage, said feeding means having its pivotal axis perpendicular to and eccentn'cally displaced from the axis of said drill such that pivoting of said means to swing said drill from a position with a heel surface trailing portion engaging said abrasive means to a position with the leading portion of said heel surface engaging said abrasive means causes said drill to be slightly withdrawn with respect to said abrasive means, and said drill holder and feeding means cooperating with said first contoured grinding surface to cut the lips and the heel surfaces with the desired lip clearance angles, and cooperating with said second contoured grinding surface to remove a portion of said heel surfaces for splitting the center of said drill; and an adjustable limiter attached to said feeding means for limiting the pivotal movement of said holder with respect to said carriage.

3. A drill grinding machine which includes: a first grinding wheel having a peripheral grinding surface beveled at an angle to the plane of said first wheel equal to the cutting angle desired on the drill; a second grinding wheel disposed parallel to said first grinding wheel and having a cylindrical peripheral surface parallel to the axis of said second wheel; means for rotatably driving said wheels; a drill holder disposed adjacent said grinding surfaces and having a removable sleeve for slidably receiving the shank of a drill therein, said sleeve having its axis normal to the axes of said wheels such that said drill is disposed parallel to the planes of said wheels with the point of said drill positioned adjacent said grinding surfaces; a stop finger extending transversely through said arm and slidably adjustable therein, said finger having a step therein for engagement with a cutting lip of the drill for limiting forward movement and rotation of said drill; a supporting carriage for supporting said drill holder, said carriage being movable in a direction parallel to the axes of the wheels to carry said drill holder therebetween; a shaft pivotally mounted on said carriage with its pivot axis parallel to the axes of said wheels; means for eccentrically mounting said drill holder on said shaft with the axis of said sleeve perpendicular to the pivot axis of said shaft, said eccentric mounting means being such that the longitudinal axis of said drill holder is disposed forward of said pivot axis when said drill holder positions said drill with its heel surface trailing edge in contact with said first wheel grinding surface and in the same vertical plane as said pivot axis when said drill holder positions said drill with its heel surface leading edge in contact with said first wheel grinding surface whereby said drill holder and mounting means cooperate with said first grinding wheel to gr nd the lips of said drill and the heel surfaces thereor with the proper lip clearance angle; and an adjustable stop screw means for limiting the pivotal movement of said shaft, said stop means cooperating with said drill holder and second vheel grinding surface to properly back cut the trailing heel surface edges of said drill to form a split center point thereon.

fl. A drill grinding machine which includes: a first grinding wheel having a peripheral grinding surface beveled at an angle to the plane of said wheel equal to the cutting angle desired on the drill; a second grinding wheel disposed parallel to said first grinding wheel and having a cylindrical peripheral grinding surface parallel to the axis of said wheel; a drill holder disposed adjacent said grinding surfaces for holding a drill with its axis parallel to the planes of said wheels and its point adjacent sari grinding surface; a stop finger mounted on said holder and so disposed as to engage with a cutting lip of said drill for limiting forward movement and rotation of said drill; a supporting carriage for supporting said drill holder, said carriage being movable to carry said drill holder between said grinding wheels; and means pivotally mounting said drill holder 'on said carriage, said mounting means having its pivot axis perpendicular to and eccentrically displaced from the EXlSOf said drill in 7 such'a manner that when said drill is positioned its heelsurface: trailing edge in engagement with the grindin'g surface of said first wheel and is then pivotally swung downwardly to engage its heel s'urface'leading edge with said first heel grinding surface, said drill pint will be ground with the proper cutting angle and lip clearance angle, and said drill holder and carriage so maintaining the positioning of said drill with respect to said wheels that properly applying said drill point to the grinding surface' of said second wheel will back cut the heel surface trailing edges and form-a split center point thereon.

5.'-A' drill grinding machine which includes: a support carriage adjustably mounted in front of a grinding wheel for movement with respect thereto; a drill holder having a removable sleeve adapted to slidably receive the shankiof a; drill therethrough to position the drill point against said grinding wheel; an arm extending through said holder substantially parallel to said sleeve and slidably and rotatably adjustable on said holder; a stop finger extending transversely through said arm and slidably adjustable therein, said finger having a ste therein for engagement with a cutting lip of the drill for limiting the forward movement and rotation of said drill; and means pivotally mounting said holder on said carriage, said mounting means having its pivot axis perpendicular to and eccentrically displaced from the axis of said drill in such a manner that pivoting of said mounting means to swing said drill from a position with the trailing portion of a heel surface engaged with said grinding wheel to a position with the leading portion of said heel surface engaged with said grinding wheel causes said drill to be automatically slightly withdrawn with respect to said grinding wheel, whereby said trailing portion is more deeply ground than said leading portion to thereby form the proper lip clearance angle on said heel surface.

6. A drill grinding machine which includes: abrasive means having a first contoured grinding surface and a second contoured grinding surface, said second grinding surface being differently contoured from said first grinding surface and being cooperatively related thereto; holder means for receiving and holding a drill in a fixed position with respect thereto; support means for supporting said abrasive means and said holder means with the point of said drill positioned adjacent said grinding surfaces, said support means allowing movement of said abrasive means and holder means relative to each other; and feeding means pivotally mounting said holder means on said support means, said feeding means having its pivotal axis eccentrically displaced from the axis of said drill such that pivoting of said feeding means to swing'said drill from a position with a heel surface trailing portion engaging said abrasive means to a position with the leading portion of said heel surface engaging said abrasive means causes said drill to be slightly withdrawn with respect to said abrasive means, and said holder means and feeding. means cooperating with said first contoured grinding surface to grind the drill lips, and the heel surfaces of said drillwith the desired lip clearance angles, and cooperating with said second contoured grinding surface to remove a particular portion of said heel surfaces for splitting the center of said drill.

7. A drill grinding'rnachine which includes: an abrasive member having a first contoured grinding surface and a second contoured grinding surface,'said grinding surface being differently contoured from said first grinding surface and being cooperatively related thereto; a holder member for receiving and holding a drill in a fixed position with respect thereto; support means for supporting said abrasive member and said holder member with the point of said drill positioned in engagement with said abrasive member, said support means allowing movement of said holder member and said abrasive member relative to each other; and feeding means pivotally mounting one a removable sleeve adapted to slideably receive the shank 8 of said members on said support means for controlling the engagement of said drill and abrasive member; said feeding means having its pivotal axis perpendicular to and eccentrically displaced from the axis of said drill such that pivoting of said feed means to vary the engagement between said abrasive member and said drill from a position with a heel surface trailing portion of said drill engaging said abrasive member to a position with the leading portion of said drill heel surface engaging said abrasive member causing said drill and abrasive member'to be slightly moved apart, and said holder member and feeding means cooperating with said first contoured grinding surface to grind the drill lips, and the heel surfaces of said drill with the desired lip clearance angles, and cooperating with said second contoured grinding surface to remove a particular portion of said heel surfaces for splitting the center of said drill.

S. A drill grinding machine which includes: a first grinding wheel having a peripheral grinding surface beveled at an angle to the plane of said wheel equal to V the cutting angle desired on the drill; a second grinding wheel disposed parallel to said first grinding wheel and having a cylindrical peripheral grinding surface parallel to the axis of said wheel; a drill holder disposed adjacent said grinding surfaces for holding a drill with its axes parallel to the planes of said wheel and its point adjacent said grinding surfaces; stop means mounted on said holder for limiting forward movement and rotation of said drill; a supporting carriage for supporting said drill holder, said carriage being movable to carry said drill holder between said grinding wheels; and means pivotally mounting said drill holder on said carriage, said mounting means cooperating with the grinding surface of said first wheel to grind said drill point lips and heel surfaces with the proper cutting angle and said drill holder and carriage so maintaining the positioning of said drill with respect to said wheels that applying said drill point to the grinding surface of said second wheel will back cut the heel surface trailing edges thereof and form a split center point thereon.

9. A drill grinding machine which includes: abrasive means having a first contoured grinding surface and a second contoured grinding surface, said second grinding surface being differently contoured from said first grindin g surface and being cooperatively related thereto; holder means for receiving and holding a drill in a fixed position relative thereto; support means for supporting said abrasive means and said drill holder with the point of said drill positioned adjacent said grinding surfaces, said support means allowing movement of said abrasive means and said holder means relative to each other; and feeding means pivotally mounting said holder means on said support means, said feeding means cooperating with said holder means and said first contoured grinding surface to grind the lips and the heel surfaces of said drill, and cooperating with said second contoured grinding surface to remove a particular portion of said heel surfaces for splitting the center of said drill point.

10. A drill grinding machine which includes: a support carriage adjustably mounted in front of a grinding wheel for movement with respect thereto; a drill holder having of a drill therethrough to position the drill point against said grinding wheel; an arm extending through said holder substantially parallel to said sleeve and slideahly and rotatably adjustable on said holder; a stop finger extending transversely through said arm and slideably adjustable therein; said finger having a step therein for engagement with a cutting lip of the drill for limiting the forward movement and rotation of said drill; and means pivotally mounting said holder on said carriage to allow said drill to be swung into engagement with said grinding wheel.

- (References on following page) References Cited in the file of this patent UNITED STATES PATENTS Landers Nov. 6, 1883 Vauclain Mar. 19, 1912 Kobis Mar. 13, 1928 Adams Feb. 22, 1938 Wells July 19, 1938 10 Raney Nov. 26, 1946 Van Wyk Oct. 3, 1950 Trippel Apr. 8, 1952 FOREIGN PATENTS Sweden Dec. 4, 1946 Great Britain June 12, 1940 

